Arrangement for actuating an element in a microlithographic projection exposure apparatus

ABSTRACT

The invention relates to arrangements for actuating an element in a microlithographic projection exposure apparatus. In accordance with one aspect, an arrangement for actuating an element in a microlithographic projection exposure apparatus comprises a first number (n R ) of degrees of freedom, wherein an adjustable force can be transmitted to the optical element in each of the degrees of freedom, and a second number (n A ) of actuators, which are coupled to the optical element in each case via a mechanical coupling for the purpose of transmitting force to the optical element, wherein the second number (n A ) is greater than the first number (n R ). In accordance with one aspect, at least one of the actuators is arranged in a node of at least one natural vibration mode of the optical element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority under 35 USC120 to, U.S. application Ser. No. 15/430,086, filed Feb. 10, 2017, nowU.S. Pat. No. 9,841,682, which is a continuation of, and claims priorityunder 35 USC 120 to, U.S. application Ser. No. 14/818,507, filed Aug. 5,2015, now U.S. Pat. No. 9,568,837, which is a continuation of, andclaims priority under 35 USC 120 to, U.S. application Ser. No.14/311,767, filed Jun. 23, 2014, now abandoned, which is a continuationof and claims priority under 35 USC 120 to U.S. application Ser. No.14/157,718, filed Jan. 17, 2014, now U.S. Pat. No. 8,786,826, whichclaims priority under 35 U.S.C. § 119(e)(1) to U.S. ProvisionalApplication No. 61/756,086 filed Jan. 24, 2013. U.S. application Ser.No. 14/311,767 and U.S. application Ser. No. 14/157,718 also claimbenefit under 35 U.S.C. § 119 to German Application No. 10 2013 201082.6, filed Jan. 24, 2013. The contents of these applications arehereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to arrangements for actuating an element in amicrolithographic projection exposure apparatus.

Prior Art

Microlithography is used for producing microstructured components suchas, for example, integrated circuits or LCDs. The microlithographyprocess is carried out in a so-called projection exposure apparatushaving an illumination device and a projection lens.

The image of a mask (=reticle) illuminated via the illumination deviceis in this case projected via the projection lens onto a substrate (e.g.a silicon wafer) coated with a light-sensitive layer (photoresist) andarranged in the image plane of the projection lens, in order to transferthe mask structure to the light-sensitive coating of the substrate.

In a projection exposure apparatus designed for EUV (i.e. forelectromagnetic radiation having a wavelength of less than 15 nm), forlack of light-transmissive materials being available, mirrors are usedas optical components for the imaging process. The mirrors can be fixedon a carrying frame and can be designed to be at least partlymanipulatable in order to enable the respective mirror to be moved forexample in six degrees of freedom (i.e. with regard to displacements inthe three spatial directions x, y and z and with regard to rotationsR_(x), R_(y) and R_(z) about the corresponding axes). In this case, theposition of the mirrors can be determined via position sensors fixed toa sensor frame.

In a projection exposure apparatus designed for EUV, mirrors designed tobe manipulatable are used both as actively deformable mirrors, in thecase of which changes in the optical properties that occur e.g. duringthe operation of the projection exposure apparatus and resultant imagingaberrations, e.g. on account of thermal influences, can be compensatedfor by active deformation, and as non-actively deformable mirrors, inthe case of which no targeted deformation is effected.

The positional control of such mirrors serves, in conjunction with asuitable actuator system (e.g. with Lorentz actuators), to keep themirrors in their position as stably as possible, such that a deviationof the mirror positions that is measured via the position sensors is assmall as possible. One approach that is possible in principle for thispurpose consists in increasing the controller gain and thus increasingthe control bandwidth. In this case, however, the problem occurs inpractice that the mirrors are not ideally rigid bodies, but rather eachhave specific natural frequencies of the mechanical structures (e.g. ofa typical order of magnitude in the range of 2-3 kHz), wherein thecorresponding natural frequency spectra for the dimensions of themirrors and of the carrying and measuring structures, the dimensionsincreasing with increasing numerical apertures, are shifted further andfurther toward lower frequencies. This applies all the more to activelydeformable mirrors, which have to be designed to be deformable and thuscompliant in a targeted manner. An excitation of the natural frequenciesvia the actuators can have the effect, however, that on account of therelatively low damping in the control loop comparatively largeamplitudes are detected by the respective position sensors, as a resultof which the stability of the control loop can be jeopardized and activepositional control can no longer be operated stably or can be operatedonly with low control quality.

With regard to the prior art, reference is made for example to U.S. Pat.No. 6,842,277 B2, US 2007/0284502 A1 and the publication “Benefits ofover-actuation in motion systems”, by M. G. E. Schneiders et al.,Proceedings of the 2004 American Control Conference (ACC 2004), Boston(2004).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide arrangements foractuating an element in a microlithographic projection exposureapparatus which enable active positional control of the element withhigher control quality.

This object is achieved in accordance with the features of theindependent patent claims.

In accordance with one aspect, the invention relates to an arrangementfor actuating an element in a microlithographic projection exposureapparatus, comprising:

-   -   a first number (n_(R)) of degrees of freedom, wherein an        adjustable force can be transmitted to the optical element in        each of the degrees of freedom; and    -   a second number (n_(A)) of actuators, which are coupled to the        optical element in each case via a mechanical coupling for the        purpose of transmitting force to the optical element;    -   wherein the second number (n_(A)) is greater than the first        number (n_(R)); and    -   wherein at least one of the actuators is arranged in a node of        at least one natural vibration mode of the optical element.

The invention is based on the concept, in particular, of performing, inan arrangement for actuating an element, in particular a mirror, an“over-actuation” insofar as the number of actuators exceeds the numberof degrees of freedom (that is to say for example for an actuation ofthe element or mirror in six degrees of freedom, at least sevenactuators are used). This additional freedom with regard to theapplication of forces to the optical element, the additional freedombeing obtained as a result of the surplus of actuators available(relative to the number of degrees of freedom) in comparison with anunambiguously statically determinate arrangement, can now be usedfurther to the effect that the forces are applied to the optical elementin such a way that the above-described excitation of natural vibrationsof the mechanical structures is reduced or even completely masked out. Afurther advantage of this over-actuation is that a better distributionof the forces is made possible on account of the higher number ofactuators.

The additional freedom obtained as a result of the over-actuationaccording to the invention can be used firstly during the positioning ofthe actuators and secondly also during the driving of the actuators(i.e. the targeted configuration of the generated line of force). As faras the positioning of the actuators is concerned, in accordance with theabovementioned approach of the invention, at least one of the actuatorsis arranged in a node of a natural vibration mode, which has theconsequence that the respective undesired natural vibration mode is notexcited, independently of the excitation of the relevant actuator.

In accordance with a further aspect, the invention relates to anarrangement for actuating an optical element in a microlithographicprojection exposure apparatus, comprising

-   -   a first number (n_(R)) of degrees of freedom, wherein an        adjustable force can be transmitted to the optical element in        each of the degrees of freedom; and    -   a second number (n_(A)) of actuators, which are coupled to the        optical element in each case via a mechanical coupling for the        purpose of transmitting force to the optical element;    -   wherein the second number (n_(A)) is greater than the first        number (n_(R)); and    -   wherein the actuators are arranged such that the actuation in        the degrees of freedom is substantially orthogonal to at least        one natural vibration mode of the optical element.

In accordance with the above approach, the actuators are arranged suchthat the actuation in the degrees of freedom is substantially orthogonalto at least one natural vibration mode. Within the meaning of thepresent application, “substantially” orthogonal should be understoodsuch that the actuation of the natural vibration modes, which becomesvisible in the transfer function of the open control loop as a weaklydamped resonance, is reduced in terms of its magnitude compared with anon-over-actuation by at least 6 dB, in particular by at least 12 dB,more particularly by at least 20 dB.

In accordance with one embodiment, the optical element is a mirror. Evenif in the further embodiments the optical element is in each case amirror of a projection exposure apparatus designed for EUV, theinvention is not restricted thereto. In this regard, the invention canalso be realized in conjunction with other optical elements, such ase.g. refractive or diffractive optical elements. In further embodiments,the invention can also be realized in a projection exposure apparatusdesigned for DUV (i.e. for wavelengths of less than 200 nm, inparticular less than 160 nm).

The mirror can be configured in particular in such a way that it isactively deformable in order to compensate for an undesirabledisturbance in the projection exposure apparatus. Such a disturbance canbe, for example, a thermal expansion on account of absorption of theradiation emitted by the (e.g. EUV) light source, and also imagingaberrations (caused by such thermal influences or in some other way).

For actively deforming a deformable mirror, use is typically made of acomparatively high number of (deformation) actuators (e.g. of the orderof magnitude of 10-100), wherein in addition the mirror is designed tobe comparatively elastic in contrast to a non-actively deformablemirror. According to the invention, these (deformation) actuators, inparticular, can be used for realizing the over-actuation describedabove. In accordance with this approach, therefore, the deformationactuators are used doubly insofar as firstly they are used for deformingthe relevant mirror and secondly they are used for controlling theposition of the mirror and in this case for generating the requisiteforces in such a way that undesired natural vibration modes of themirror are excited to a lesser extent or are not excited at all. Inother words, therefore, the deformation actuators additionally performthe function of the positioning actuators (exclusively present in thecase of a non-actively deformable mirror).

In accordance with a further embodiment, the mirror can also be anon-actively deformable mirror.

In accordance with one embodiment, the arrangement furthermore comprisesa third number (n_(S)) of sensor elements for determining the locationand/or position of the optical element. In accordance with oneembodiment, in this case the third number (n_(S)) of sensor elements isgreater than the first number (n_(R)) of degrees of freedom.

In accordance with this aspect of the invention, in particular inconjunction with a non-actively deformable mirror, therefore, a surplusn_(S) (i.e. at least n_(R)+1) of sensors can also be provided relativeto the number of degrees of freedom (n_(R)) that exist in thepositioning of the optical element. This further concept according tothe invention, which is equivalent to the above-described over-actuationin terms of control engineering, is also designated as “over-sensing”hereinafter analogously to over-actuation. The additional freedomobtained as a result of the surplus of sensors can be used for choosingan arrangement of the sensors in such a way that specific naturalfrequencies or natural vibration modes are not even detected by thesensor system in the first place, with the consequence that thepositional control cannot react to such natural frequencies. The conceptof over-sensing has the further advantage that forces are still appliedto the optical element or the mirror in a statically governed manner andinherent or undesired deformations of the optical element or mirror arethus avoided.

The above-described concept of “over-sensing” is also advantageousindependently of the concept of “over-actuation”.

In accordance with a further aspect, therefore, the invention alsorelates to an arrangement for actuating an optical element in amicrolithographic projection exposure apparatus, comprising:

-   -   a first number (n_(R)) of degrees of freedom, wherein an        adjustable force can be transmitted to the optical element in        each of the degrees of freedom; and    -   a third number (n_(S)) of the sensor elements for determining        the location and/or position of the optical element;    -   wherein the third number (n_(S)) is greater than the first        number (n_(R)).

The arrangement according to the invention can be designed, inparticular, for actuating an optical element in a microlithographicprojection exposure apparatus designed for EUV.

The invention can furthermore be used both in the illumination deviceand in the projection lens of a microlithographic projection exposureapparatus.

In accordance with one embodiment, the first number (n_(R)) of degreesof freedom is at least three, in particular six.

The invention furthermore relates to a microlithographic projectionexposure apparatus comprising an arrangement having the featuresdescribed above.

In accordance with a further aspect, the invention relates to a methodfor actuating an optical element in a microlithographic projectionexposure apparatus,

-   -   wherein adjustable forces are transmitted to the optical element        in a first number (n_(R)) of degrees of freedom;    -   wherein the force transmission is effected via a second number        (n_(A)) of actuators;    -   wherein the second number (n_(A)) is greater than the first        number (n_(R)); and    -   wherein at least one of the actuators is arranged in a node of        at least one natural vibration mode of the optical element.

In accordance with a further aspect, the invention also relates to amethod for actuating an optical element in a microlithographicprojection exposure apparatus,

-   -   wherein adjustable forces are transmitted to the optical element        (100, 200) in a first number (n_(R)) of degrees of freedom;    -   wherein the force transmission is effected via a second number        (n_(A)) of actuators;    -   wherein the second number (n_(A)) is greater than the first        number (n_(R)); and    -   wherein the actuation in the degrees of freedom is substantially        orthogonal to at least one natural vibration mode of the optical        element.

In accordance with one embodiment, the optical element is activelydeformed by the adjustable forces.

In accordance with one embodiment, the position of the optical elementis manipulated by the adjustable forces.

In accordance with one embodiment, a third number (n_(S)) of sensorelements are used to determine the location and/or position of theoptical element. In this case, in particular, the third number (n_(S))can be greater than the first number (n_(R)).

The invention therefore also relates to a method for positioning and/oractively deforming an optical element in a microlithographic projectionexposure apparatus,

-   -   wherein a controllable force is transmitted to the optical        element in a first number (n_(R)) of degrees of freedom; and    -   wherein a third number (n_(S)) of sensor elements are used to        determine the location and/or position of the optical element;    -   wherein the third number (n_(S)) is greater than the first        number (n_(R)).

In this case, the method can respectively comprise in particular thefollowing steps:

-   -   determining at least one imaging aberration in the projection        exposure apparatus; and    -   positioning and/or actively deforming the optical element in        such a way that the imaging aberration is at least partly        compensated for.

Further configurations of the invention can be gathered from thedescription and the dependent claims.

The invention is explained in greater detail below on the basis ofexemplary embodiments illustrated in the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures:

FIGS. 1A-1B show schematic illustrations for elucidating one approachaccording to the invention in conjunction with a non-actively deformablemirror;

FIG. 2 shows a schematic illustration for elucidating one approachaccording to the invention in conjunction with an actively deformablemirror;

FIGS. 3-4A-4C show schematic illustrations for elucidating oneembodiment on the basis of the example of positional control of avibratory body;

FIG. 5 shows a diagram for elucidating a control loop on the basis ofthe example of an actively deformable mirror with realization of theover-actuation according to the invention;

FIG. 6 shows a diagram for elucidating a control loop on the basis ofthe example of an actively deformable mirror with realization of theover-sensing according to the invention;

FIG. 7 shows a diagram for elucidating a control loop on the basis ofthe example of an actively deformable mirror with realization of astatically determinate I-controller; and

FIG. 8 shows a schematic illustration of an exemplary construction of amicrolithographic projection exposure apparatus which is designed foroperation in the EUV and in which the present invention can be realized.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A-1B firstly show schematic illustrations for elucidating oneapproach according to the invention in conjunction with a non-activelydeformable mirror.

In accordance with FIG. 1A, a mirror 100 to be held in a definedposition is conventionally mounted isostatically by virtue of the factthat three actuators 111, 112 and 113 having a force direction or drivedirection perpendicular to the mirror 100 are used to position themirror 100 in the three degrees of freedom z, R_(x) and R_(y) (i.e. withregard to displacement in the spatial direction z and rotation about thex- and y-axis, respectively). With exactly these three actuators 111,112 and 113, the three degrees of freedom z, R_(x) and R_(y) arestatically determinate. As likewise explained here with reference toFIGS. 3 and 4, however, these three actuators 111, 112 and 113 canexcite elastic natural frequencies or natural vibration modes of themirror 100.

As indicated in FIG. 1B, a higher number (in the example n_(A)=4) ofactuators 111, 112, 113 and 114 relative to the number of degrees offreedom (in the example the three degrees of freedom z, R_(x) and R_(y))is now used according to the invention, as likewise explained in evengreater detail with reference to FIGS. 3 and 4, the actuators 111-114being positioned in such a way that no undesired excitation orassociated disturbance of the positional control takes place for somenatural frequencies or natural vibration modes of the mirror 100.

FIG. 2 serves for clarifying the concept according to the invention inconjunction with an actively deformable mirror 200, likewise merelyindicated schematically. In accordance with FIG. 2, a comparatively highnumber (e.g. 10, 100 or more) of deformation actuators 211, 212, . . .serve for actively deforming the deformable mirror 200, wherein themirror 200 is simultaneously designed to be comparatively elastic inorder to enable an active deformation. According to the invention, thedeformation actuators 211, 212, . . . are used doubly insofar as firstlythey serve for deforming the mirror 200 and secondly they serve, by wayof the over-actuation described above, to configure the positionalcontrol of the mirror 200 in such a way that an undesired excitation ofnatural frequencies or natural frequency modes of the mirror 200 as faras possible does not occur.

The principle and the functioning of the over-actuation appliedaccording to the invention to an optical element such as a mirror, forexample, are explained below on the basis of a specific exemplaryembodiment with reference to the schematic illustrates in FIGS. 3 and 4.In this case, the movement of the optical element in FIGS. 3 and 4 isrestricted to a translational and a rotational degree of freedom, forthe sake of simplicity, and the system is subdivided or discretized intothree nodes 310, 320, 330 for describing the vibration capability,wherein each of the nodes 310, 320, 330 has a respective translationaldegree of freedom q₁, q₂ and q₃ and a respective rotational degree offreedom φ₁, φ₂ and φ₃.

Furthermore, in accordance with FIG. 3, the same mass m is assigned toeach node 310, 320, 330, wherein the nodes 310, 320, 330 are associatedwith the same stiffness k.

The system discretized in a simplified manner in accordance with FIG. 3shows, as illustrated schematically in FIGS. 4A-4C, three vibrationmodes, wherein a first vibration mode is the translation of the rigidbody (FIG. 4A), a second vibration mode is the rotation of the rigidbody (FIG. 4B) and a third vibration mode is a first bending vibrationof the rigid body (FIG. 4C).

$\begin{matrix}{\begin{pmatrix}q_{1} \\q_{2} \\q_{3}\end{pmatrix} = {\begin{pmatrix}1 \\1 \\1\end{pmatrix} = q_{m\; 1}}} & (1) \\{\begin{pmatrix}q_{1} \\q_{2} \\q_{3}\end{pmatrix} = {\begin{pmatrix}{+ 1} \\0 \\{- 1}\end{pmatrix} = q_{m\; 2}}} & (2) \\{\begin{pmatrix}q_{1} \\q_{2} \\q_{3}\end{pmatrix} = {\begin{pmatrix}{+ 1} \\{- 1} \\{+ 1}\end{pmatrix} = q_{m\; 3}}} & (3)\end{matrix}$

Conventionally, two actuators could then be chosen for a staticallydeterminate actuation, via which actuators the rigid-body translationand the rigid-body rotation can be actuated, for which purpose, in thespecific case, one actuator (for applying the force F₁) can be arrangedat the node 310 and the other actuator (for applying the force F₃) canbe arranged at the node 330. For the control of the translation andrespectively rotation by a controller, a transformation matrix T_(a) canusually be used which generates a desired translational force f and adesired torque M, via these two actuators:

$\begin{matrix}{{\begin{pmatrix}f_{1} \\f_{2} \\f_{3}\end{pmatrix} = {T_{a}\begin{pmatrix}f \\M\end{pmatrix}}},{{{where}\mspace{14mu} T_{a}} = \begin{pmatrix}\frac{1}{2} & \frac{1}{2l} \\0 & 0 \\\frac{1}{2} & \frac{1}{2l}\end{pmatrix}}} & (4)\end{matrix}$

wherein the following holds true:

$\begin{matrix}{{{q_{m\; 1}^{T} \cdot T_{a}} = \begin{pmatrix}1 & 0\end{pmatrix}},{{q_{m\; 2}^{T} \cdot T_{a}} = \begin{pmatrix}0 & \frac{1}{l}\end{pmatrix}},{{q_{m\; 3}^{T} \cdot T_{a}} = \begin{pmatrix}1 & 0\end{pmatrix}}} & (5)\end{matrix}$

Upon checking how the vibration modes of the system are excited in thecase of such a statically determinate actuation via the chosen actuatorsand using the abovementioned transformation matrix, it is then evidentthat the force f excites the translational rigid-body mode (mode 1) asdesired and the torque M excites the rotational rigid-bodied mode (mode2), but the force f also additionally excites the bending mode (mode 3)(since, as can be seen from (5), the bending mode (=mode 3) is visiblein the translational axis). Consequently, the bending mode is alsovisible in the transfer function of the control loop for thetranslational movement and may possibly lead undesirably to a limitationof the bandwidth that can be set.

The problem described above can now be rectified via the over-actuationaccording to the invention as follows. For this purpose, an additionalactuator is provided in the exemplary embodiment, the additionalactuator being arranged at the node 320 for applying the force F₂ inaccordance with FIG. 3. Consequently, three actuators are available forgenerating the forces for translation and rotation, such that comparedwith the above-described statically determinate actuation via twoactuators, additional freedom is obtained with regard to the design ofthe transformation matrix Ta, since the transformation matrix Ta is nowno longer uniquely determinate. In order to use the freedom additionallyobtained as a result, the elements of the transformation matrix Ta arepreferably chosen such that the force f and the torque M still actuateonly the corresponding (translational or rotational) rigid-body degreeof freedom, but the force f can no longer excite the bending mode.

In the specific exemplary embodiment, the transformation matrix Ta canbe chosen as follows:

$\begin{matrix}{{\begin{pmatrix}f_{1} \\f_{2} \\f_{3}\end{pmatrix} = {T_{a}\begin{pmatrix}f \\M\end{pmatrix}}},{{{where}\mspace{14mu} T_{a}} = \begin{pmatrix}\frac{1}{3} & \frac{1}{2l} \\\frac{1}{3} & 0 \\\frac{1}{3} & \frac{1}{2l}\end{pmatrix}}} & (6)\end{matrix}$

wherein the following holds true:

$\begin{matrix}{{{q_{m\; 1}^{T} \cdot T_{a}} = \begin{pmatrix}1 & 0\end{pmatrix}},{{q_{m\; 2}^{T} \cdot T_{a}} = \begin{pmatrix}0 & \frac{1}{l}\end{pmatrix}},{{q_{m\; 3}^{T} \cdot T_{a}} = \begin{pmatrix}0 & 0\end{pmatrix}}} & (7)\end{matrix}$

As can be seen from (7), the bending mode (=mode 3) is no longer visiblein the translational axis.

FIG. 5 shows a diagram for elucidating the construction and function ofa control loop for the case of an actively deformable mirror with therealization of the above-explained concept of over-actuation accordingto the invention. In this case, n_(R) denotes the number of positionallycontrolled rigid-body degrees of freedom and n_(A) denotes the number ofpositionally controlled actuators, wherein the number of actuatorsexceeds the number of degrees of freedom, that is to say n_(A)>n_(R)holds true.

In accordance with FIG. 5, the desired values for the mirror positionare fed to a position controller 510, which generates a statictransformation matrix T_(a) for the n_(R) positionally controlledrigid-body degrees of freedom. On the basis of the transformation matrixT_(a) and a driving signal for the mirror deformation, actuators 520 foractuating the mirror 530 are driven with position determination via theposition sensors 540. The resultant static transformation matrix T_(a)is in turn fed to the position controller 510, etc.

FIG. 6 shows an analogous diagram for elucidating a control loop for thecase of an actively deformable mirror with the realization of theconcept of “over-sensing” according to the invention, likewise explainedabove. In this case, n_(R) denotes the number of positionally controlledrigid-body degrees of freedom and n_(S) denotes the number of sensors,wherein the number of sensors exceeds the number of degrees of freedom;n_(S)>n_(R) holds true.

FIG. 7 shows a further exemplary embodiment of the invention, whereincomponents that are analogous or substantially functionally identical toFIG. 5 are designated by reference numerals increased by “200”. In thiscase, once again n_(R) denotes the number of positionally controlledrigid-body degrees of freedom and n_(A) denotes the number ofpositionally controlled actuators, wherein the following holds true:n_(A)>n_(R).

The exemplary embodiment in FIG. 7 takes account of the circumstancethat the over-actuation applied according to the invention can lead toundesired deformations of the optical element. The cause of theundesired deformations is that the position controller generally exertsboth dynamic and small static forces in order to keep the opticalelement stably in position. The static forces can be position- andtime-dependent. The overdeterminate application of the variable staticforces to an overdeterminate number of force application points(actuators) can then lead to undesired deformations of the opticalelement.

This problem can be solved as follows by the concept described withreference to FIG. 7: The position controller is typically a PID-likecontroller, i.e. a controller whose dynamic behavior has a proportionalcomponent (P component), a derivative component (D component) and anintegral component (I component). The I component generates the staticforces, whereas the P component and the D component generate the dynamicforces. If the I component is then separated from the PD component andapplied statically determinately to a smaller statically determinatesubset (n_(R)) of actuators, the static forces are always appliedstatically determinately to a statically determinate number of forceapplication points, with the result that the undesired deformationsdescribed above are avoided.

FIG. 8 shows a schematic illustration of a microlithographic projectionexposure apparatus which is designed for operation in the EUV and inwhich the present invention can be realized, for example.

The projection exposure apparatus in accordance with FIG. 8 comprises anillumination device 6 and a projection lens 31. The illumination device6 comprises, in the light propagation direction of the illuminationlight 3 emitted by a light source 2, a collector 26, a spectral filter27, a field facet mirror 28 and a pupil facet mirror 29, from which thelight impinges on an object field 4 arranged in an object plane 5. Thelight emerging from the object field 4 enters into the projection lens31 with an entrance pupil 30. The projection lens 31 has an intermediateimage plane 17, a first pupil plane 16 and a further pupil plane with astop 20 arranged therein. The projection lens 31 comprises a total of 6mirrors M1-M6. M6 denotes the last mirror relative to the optical beampath, the mirror having a through-hole 18. M5 denotes the penultimatemirror relative to the optical beam path, the mirror having athrough-hole 19. A beam emerging from the object field 4 or reticlearranged in the object plane passes onto a wafer, arranged in the imageplane 9, after reflection at the mirrors M1-M6 in order to generate animage of the reticle structure to be imaged.

The arrangement according to the invention can be used for positioningand/or actively deforming one or a plurality of mirrors in theprojection lens 31 and/or in the illumination device 6.

Even though the invention has been described on the basis of specificembodiments, numerous variations and alternative embodiments are evidentto a person skilled in the art, e.g. via combination and/or exchange offeatures of individual embodiments. Accordingly, it goes without sayingfor a person skilled in the art that such variations and alternativeembodiments are concomitantly encompassed by the present invention, andthe scope of the invention is restricted only within the meaning of theaccompanying patent claims and the equivalents thereof.

1.-20. (canceled)
 21. An arrangement configured to actuate an opticalelement of a microlithographic projection exposure apparatus, theoptical element configured so that an adjustable force is transmittableto the optical element in a first number of degrees of freedom, thearrangement comprising: a second number of actuators; wherein: thesecond number is greater than the first number; for each of the secondnumber of actuators, the actuator is coupled to the optical element viaa mechanical coupling to transmit force to the optical element; theactuators are arranged so that, when at least one natural vibration modeof the optical element is actuated, a magnitude of a transfer functionof an open control loop at a frequency of the at least one naturalvibration mode is reduced by at least six dB compared with anarrangement in which the second number is not greater than the firstnumber.
 22. The arrangement of claim 21, wherein the actuators arearranged so that, when the at least one natural vibration mode of theoptical element is actuated, the magnitude of the transfer function ofthe open control loop at the frequency of the at least one naturalvibration mode is reduced by at least 12 dB compared with thearrangement in which the second number is not greater than the firstnumber.
 23. The arrangement of claim 21, wherein the actuators arearranged so that, when the at least one natural vibration mode of theoptical element is actuated, the magnitude of the transfer function ofthe open control loop at the frequency of the at least one naturalvibration mode is reduced by at least 20 dB compared with thearrangement in which the second number is not greater than the firstnumber.
 24. The arrangement of claim 21, wherein the optical elementcomprises a mirror.
 25. The arrangement of claim 24, wherein the mirroris actively deformable to compensate for an undesirable disturbance inthe microlithographic projection exposure apparatus.
 26. The arrangementof claim 24, wherein the mirror is a non-actively deformable mirror. 27.The arrangement of claim 21, further comprising a third number of sensorelements configured to determine at least one parameter selected fromthe group consisting of a location of the optical element and a positionof the optical element.
 28. The arrangement of claim 27, wherein thethird number is greater than the first number.
 29. The arrangement ofclaim 21, wherein at least one actuator comprises a Lorentz actuator.30. The arrangement of claim 21, wherein the first number of degrees offreedom is at least three.
 31. The arrangement of claim 21, wherein thefirst number of degrees of freedom is six.
 32. The arrangement of claim21, wherein the arrangement is configured so that the optical element isactively deformed by the adjustable forces.
 33. The arrangement of claim21, wherein the arrangement is configured so that a position of theoptical element is manipulated via the adjustable forces.
 34. Thearrangement of claim 21, wherein the microlithographic projectionexposure apparatus comprises an EUV microlithographic projectionexposure apparatus.
 35. An apparatus, comprising: an optical element;and an arrangement configured to actuate the optical element, theoptical element configured so that an adjustable force is transmittableto the optical element in a first number of degrees of freedom, thearrangement comprising a second number of actuators; wherein: the secondnumber is greater than the first number; for each of the second numberof actuators, the actuator is coupled to the optical element via amechanical coupling to transmit force to the optical element; theactuators are arranged so that, when at least one natural vibration modeof the optical element is actuated, a magnitude of a transfer functionof an open control loop at a frequency of the at least one naturalvibration mode is reduced by at least six dB compared with anarrangement in which the second number is not greater than the firstnumber; and the apparatus is a microlithographic projection exposureapparatus.
 36. The apparatus of claim 35, comprising an illuminationdevice, wherein the optical element is in the illumination device. 37.The apparatus of claim 35, comprising a projection lens, wherein theoptical element is in the projection lens.
 38. The apparatus of claim35, wherein the optical element comprises a mirror.
 39. An apparatus,comprising: an illumination device; a projection lens; a mirror; and anarrangement configured to actuate the mirror, the mirror configured sothat an adjustable force is transmittable to the mirror in a firstnumber of degrees of freedom, the arrangement comprising a second numberof actuators; wherein: the second number is greater than the firstnumber; for each of the second number of actuators, the actuator iscoupled to the mirror via a mechanical coupling to transmit force to themirror; the actuators are arranged so that, when at least one naturalvibration mode of the mirror is actuated, a magnitude of a transferfunction of an open control loop at a frequency of the at least onenatural vibration mode is reduced by at least six dB compared with anarrangement in which the second number is not greater than the firstnumber; the mirror is in the illumination system or the projection lens;and the apparatus is a microlithographic projection exposure apparatus.40. The apparatus of claim 39, wherein the microlithographic projectionexposure apparatus comprises an EUV microlithographic projectionexposure apparatus.